Tension



Jan. 24. 1956 J. o. NIGRA ETAL APPARATUS FOR TRAINING TWISTED CONVEYOR BELTS 3 Sheets-Sheet 1 Filed June 28, 1952 INVENTORS JOHN D. NIGRA GENO COLOMBO ATTORNEY Jan. 24, 1956 J. 0. NIGRA ETAL 2,732,058

APPARATUS FOR TRAINING TWISTED CONVEYOR BELTS Filed June 28, 1952 a Sheets-Sheet 2 JOHN D. NIGRA GENO COLOMBO IN VEN TORS ATTORNEY Jan. 24, 1956 N R ETAL 2,732,058

APPARATUS FOR TRAINING TWISTED CONVEYOR BELTS Filed June 28, 1952 3 Sheets-Sheet 3 FIG.7.

STRAIN IN INCHES HIGH BELT WIDTH LOW TENSION 3" INGREMENTS TENSION EDGE EDGE MI 0F STRAIN IN INCHES 8 HIGH BELT WIDTH Low TENSION 5 TENSION EDGE 3 INGREMENT EDGE FIGS.

STRAIN IN INCHES HIG H BE LT WIDTH TEINOSVIION TENSION EDGE 3 INGREDIENTS EDGE INVENTORS JOHN D. NIGRA By GENO COLOMBO ATTORNEY United States Patent C) APPARATUS FOR TRAINING TWISTED CONVEYOR BELTS John D. Nigra, Negaunee, and Geno Colombo, Princeton, Micln, assignors to Chain Belt Company, Milwaukee, Wis., a corporation of Wisconsin Application June 28, 1952, Serial No. 296,142

14 Claims. (CLIPS-184) This invention relates to training means for conveyor belts, particularly conveyor belts in which the slack or return side is inverted in order to prevent contact between the load carrying side of the belt and the return idlers.

When conveying certain types of materials on conventional conveyor belts, difliculty is experienced with fines and sticky residue adhering to the carrying surface of the belt. Excellent examples of such substances are various metallic and non-metallic ores and coal, which as mined and after crushing contain an appreciable quantity of abrasive power and sand size particles which may become imbedded in the belt cover or adhere thereto. These particles cause no appreciable damage to the carrying side of the belt on its load carrying run, but when the belt passes over the head pulley and starts its return run, this load carrying or dirty side of the belt comes into contact with some of the snub pulleys and all of the return idlers. These pulleys and idlers become coated with abrasive and/ or sticky particles from the belt and damaging wear of the conveyor belt and the snub pulleys and return idlers results. This wear is appreciable and may reduce the life of theatfected parts to a fraction of their normal life. Since the cost of the aforesaid parts is substantial, this difiiculty with wear has actually created unsurmountable problems in many potential conveyor installations, and has thereby limited the use of belt conveyors in some applications.

Many substances that are otherwise suitable for belt conveyance, such as ores, contain an appreciable quantity of moisture due to the presence of subterranean streams in the areas from which they are removed. This moisture causes trouble in two important respects. First, the moisture forms a binder for the abrasive powdery portion of the ore which enhances the abrasive action and also adds to the tendency for ore particles to build up on the moving parts of the conveyor. I

Second, economics dictates that the mines operate throughout the year if possible, which in many cold climates causes conveyor failure because the moisture freezes, causing an even more rapid build up of ice and trapped ore particles on the conveyor belt, snub pulleys and return idlers. Also, the belt may freeze in place when it is shut down and upon restarting the cover will be ripped from the belt.

Previous efforts to remove the accumulation of particles from the belt have met with limited success because the covering of the belt will not stand the abuse of scrapers and brushes pressing against it with sufiicient force to affect a substantial cleaning. Washing the belt with sprays of water likewise has proved unsatisfactory because of the difiiculty of supplying and disposing of the wash water.

Recently it has been proposed that the major portion of the aforesaid difficulty would be overcome if the belt could be inverted on its lower run so that the clean side of the belt would contact the snub pulleys and 'idle'rs on the return run as is the case on the loadcarrying run. This inversion of the return run of the belt makesit possible to reduce the number of return idlers contacting the 2,732,058 Patented Jan. 24, 1956 dirty side of the belt to zero and the number of snub pulleys contacting the dirty belt side to a minimum, the exact number depending upon the design of the conveyor. 'The snub pulleys which must contact the dirty side of the belt may all be fiat-faced metallic pulleys, which type can be very effectively kept clean of build up by scrapers or other types of wipers.

There are various ways in which the twist may be put into the belt, but the most generally useful type of twist is a full twist in a straight run of the belt, the twisting being accomplished in a substantially horizontal plane.

The stresses which are placed upon a belt as it passes through the twisted portion depend in part upon the plane in which the twist is accomplished. Two cases may be considered to illustrate the types of stresses that are encountered. The first case is a full 180 twist in a vertical or substantially vertical direction. In this case the centerline of the belt follows a straight line which is tangent to the entering and leaving twist pulleys at the point of contact of the center of the belt with these pulleys. The belt edges follow a substantially helical generation about the centerline of the belt as an axis. It is readily apparent that the belt edges must, therefore, travel a greater distance than the center of the belt and are thereby stretched and subjected to a greater stress than is found in the fibers adjacent to the center of the belt.

The second case, that of a full 180 twist in a substantially horizontal plane, is the most useful twist application because of a lesser requirement for head space than in the case of a twist in a vertical plane. In this case the centerline of the belt is not a straight line because the weight of the belt introduces a catenary sag, causing the centerline of the belt to trace what has been found to be a generally parabolic line, having a sag at the center less than that which would result from a true catenary sag. This sagging of the belt induces greater stress in the lowermost edge of the belt as it passes through the con tral part of the twist section, so that this edge of the belt is stressed to a greater extent than is the uppermost edge of this portion of the belt.

This unequal distribution of stress across the belt as it passes through the twist section has been found to pass beyond the outgoing twist pulley and even beyond subsequent pulleys. The result of this unequal stress distribution across the belt is to create training problems, it being the tendency of the belt to move across the pulleys toward the low tension belt edge.

it is well known that a crowned pulley may be used to train a flat belt, the theory being that the crown produces in any belt attempting to run oil center unequal stresses across the belt, the resultant of which urges the belt back to the center of the pulley. 1n the case of a twisted belt however, the stresses across the belt are already unequal and the effect of introducing further unequal stresses by a crowned pulley is to cause the belt to behave erratically and not train in the manner normally expected from a crowned pulley.

it is also known that-a flat belt can be trained on an idler or snub pulley by advancing the end of the idler or pulley toward which the belt tends to run, and this method of training twisted belts has been found to be satisfactory as long as the belt is running under a relatively constant load. However, in the case of a twisted belt, it hasbeen found that a change in belt tension due to starting the belt or adding or removing a load from the belt causes a redistribution of stress transversely across the belt re resulting in serious fleeting across the outgoing twist pulley, which fleeting may effect belt training on the head and tail and other pulleys and idlers.

' Accordingly it is the primary object of this invention to provide means for training a twisted conveyor belt which will confine to very small limits fleeting of the belt due to a change in the load on the belt.

Cross winds frequently cause belt fleeting in installations where the belt operates in the open. The twisted section of a belt is particularly subject to this difliculty because a portion of the flat part of the belt is exposed to the wind. Another object of this invention is to limit the fleeting action caused by wind and to limit billowing of the twisted section which would cause a further redistribution of stresses through the twisted section.

It is a further object of this invention to provide belt training means for twisted belts which may be inoperative when the belt is running in its normal position but which will become operative and limit fleeting action caused by loads above and below that for which the belt was normally trained.

It is a still further object of this invention to provide a training means as aforesaid which will operate for long periods of time without becoming clogged with material picked up from the dirty side of the belt.

According to this invention, belt twisting and training is accomplished by passing the belt around or over or under pulleys spaced apart so as to form the limits of the twist section. Substantially midway between these ingoing and outgoing twist pulleys a double roll assembly is placed, the axes of the rolls being substantially perpendicular to a line tangent to the circumferences of the ingoing and outgoing twist pulleys at the point where the center of the belt leaves and arrives at those pulleys. One of the rolls of the aforesaid double roll assembly is located adjacent the clean side of the belt and the other adjacent the dirty side of the belt in a straddling relationship to the belt. Clearance between the periphery of the rolls and the belt surfaces is normally allowed so that when the belt occupies the position for which it was initially trained it does not contact the rolls. A change from normal belt path causes the belt to contact one or the other of the rolls and thereby limits the extent to which the belt may fleet on the outgoing twist pulley, in a manner which is hereafter more fully described.

The invention may be more fully understood by reference to the drawings in which:

Figure l is an elevation of a troughed conveyor in which the return strand has been inverted by means of two 180 twists, each in the same direction, said twists being adjacent its head and tail ends, each twist section being trained by the double roll training assembly;

Figure 2 is an enlarged view of the twist section adjacent the left or tail end of the conveyor shown in Fig. 1 and shows the entering and leaving twist pulleys and the double roll guide assembly properly oriented with respect to the belt centerline;

Figure 3 is a section on line 33 of Fig. 1 looking in the direction of the arrows and shows the cross frame members and mounting for the ingoing tail twist pulley;

Figure 4 is a section (shortened vertically to facilitate illustration) on the line 44 of Fig. 1 looking in the direction of the arrows and shows the double roll guide assembly oriented with respect to a cross section through the belt;

Figure 5 is a side view of the guide assembly shown in Fig.4;

Figure 6 shows a modified form of guide assembly in which the roll adjacent the dirty side of the belt is of the spiral, self-cleaning type; and

Figures 7, 8 and 9 are strain diagrams illustrating the variation in stress across a section of the conveyor belt caused by changes in the load carried by the belt.

Referring to the drawings, Fig. 1 illustrates a conveyor installation in which the lower strand of the belt has been inverted. The conveyor is supported upon longitudinal truss members or stringers 11 spaced apart by cross members 12 (Fig. 3) and supported vertically by means of frame members or bents 13 which may be attached at their lower ends to the foundation or floor 14. Material to be conveyed is loaded on the belt 15 through a hopper 16 and is confined adjacent the loading point by skirt boards 17 which prevent material from falling over the edges of the belt. The upper or load carrying run 18 of the belt travels in the direction of the arrow in Fig. 1 over conventional troughing idlers 19 and is driven by a motor 20 which turns the head pulley 21 by means of a chain and sprocket drive 22. Material loaded on the belt is discharged over the head pulley 21 into a receiving hopper 49.

After passing around the head pulley 21 the direction of the belt is changed by passing it over a snub or bend pulley 23 from which the belt passes around a weighted gravity takeup pulley 24 arranged to provide a fixed load upon the belt in a conventional manner, the details of which are not illustrated.

From the gravity takeup pulley 24 the belt passes over an ingoing twist pulley 25, is twisted in a counterclockwise direction (looking in the direction of belt travel) and then passes over an outgoing twist pulley 26.

It may be noted that a guide assembly 27 is located midway between the ingoing twist pulley 25 and the outgoing twist pulley 26, straddling that portion of the twist section which is substantially vertical. The details of this guide assembly 27 will be described subsequently in greater detail.

Between the outgoing twist pulley 26 at the head end of the conveyor and the ingoing twist pulley 28 at the tail end of the conveyor the lower or return run of the belt passes, in the direction of the arrow in Fig. 1, over conventional flat return idler rolls 29 and it may be noted that the clean side of the belt is in contact with these idlers.

A second 180 counter-clockwise twist (again looking in the direction of belt travel) is placed in the belt adjacent the tail end of the return run between pulleys 28 and 30 and a second guide assembly 27 similar to the one shown in the head end twist section is placed medially between the tail twist pulleys 28 and 30. From the outgoing tail twist pulley 30 the belt passes around the tail pulley 31 and again emerges upon the load carrying run 19.

Figure 2 is an enlarged view of the twisted section adjacent the tail end of the conveyor shown in Fig. l. The ingoing tail twist pulley 28 is rotatably mounted on a pair of oppositely disposed vertical frame members 13 (see Fig. 3) by means of bearings 32 at each end of its axial shaft 33 which lies transverse to the direction of belt travel. Normally the stresses across the width of the belt will be substantially uniformly distributed as the belt approaches this ingoing twist pulley 28 having become so during the passage of the belt along the re turn run. The outgoing tail twist pulley 30 is adjustable by means of conventional wedge base pillow blocks 34 adjustably attaching the pulley shaft 35 to a pair of oppositely disposed frame members 13.

Longitudinal adjustment of this pulley 30 may be affected by means of the wedges in the pillow block base and in general it will be necessary to advance the end of the pulley nearest the low tension edge of the belt forwardly in the direction of belt travel so that the axis of the pulley is displaced slightly from a position transverse to the belt. It may be noted in Fig. 2 that medially between the pulleys 28 and 30 a double roll guide assembly 27 is placed in straddling relationship to the belt, which cooperates with the adjustable outgoing twist pulley 30 to train the belt and minimize fleeting of the belt on the outgoing twist pulley 30.

The details of construction of the guide assembly 27 are best illustrated in Figures 4 and 5. In Fig. 4 a vertcal cylindrical roll 36 is placed adjacent to the clean side of the belt while a similar vertical cylindrical roll 37 is placed adjacent the dirty side of the belt. It may be seen that clearance is provided between the peripheries of the rolls and the belt surfaces so that the greases rolls do not contact the belt when the belt is in its normal position as illustrated in Fig. 4.

The vertical rolls 36 and 37 are carried by stub shafts 38 rotatably retained in bearings 39 securely fastened at the top and bottom by transverse cantilever supports 40. The supports 40 are supported by two vertical stanchion members 41, each of which may be adjusted transversely along an upper cross beam 42 aifixed to the stringers 11 and a lower cross beam 43 fixed to the floor 14 of the conveyor structure. Such transverse adjustment is accomplished by loosening retaining screws 44 which normally clamp the upper ends of the stanchion members 41 to the upper cross beam 42 and by loosening the retaining screws 45 which normally clamp the lower end of the stanchion members 41 to the lower cross beam 43. With the retaining screws loosened, set screws 46, which are fastened to the stanchions 41 at their inner ends, may be adjusted as desired to cause independent transverse movement of either end of both vertical stanchions 41 in either direction. Also by removing screws 44 and 45, and by sliding the set screws 46 out of the slots 50 in brackets 51, either or both of the stanchions and the roll which it supports may be completely removed, which feature facilitates removal of the endless belt from the conveyor structure without cutting it, and removing the rolls for replacement or repair.

Since the roll 37 is adjacent to the dirty side of the belt it will tend to accumulate abrasive matter carried by the belt and in order to prevent a build up of this material a scraper 47 is provided to contact the periphery of the roll 37 and scrape it clean as it rotates.

It may be seen in Figs. 1 and 2 that the guide assembly is positioned so that the axes of the rolls 36 and 37 are substantially normal or perpendicular to the longitudinal centerline of the belt, preferably at the midpoint of the twisted section.

Figure 6 illustrates a modified form of guide assembly in which the roll 37 adjacent the dirty side of the belt has been replaced by a spiral type cylindrical idler 48 which will gently knead the belt and thereby be selfcleaning when rotated by contact with the belt. A spiral idler roll of the type illustrated is described in United States Patent 2,391,178 issued to L. B. McKnight.

Figures 7,8 and 9 are curves illustrating the unequal distribution of stresses which occur in the twist section of a conveyor belt and are reproduced from measure ments made on the tail end twist of a thirty-six inch belt twisted in a substantially horizontal plane. The strain measurements of Figure 8 were taken transversely across the belt at the midpoint of the twist halfway between the ingoing and outgoing twist pulleys. Figure 7 is the strain approximately one-third into the twist section or one-third of the distance between ingoing and outgoing twist pulleys, while Figure 9 is the strain approximately two-thirds of the distance into the twist section or two-thirds of the distance between the ingoing and outgoing twist pulleys. In the curves the characteristic distribution of stress (as exemplified by measured belt strain) through the twisted section is illustrated and it may be seen that the stress is lowest at the center of the belt and rises more or less parabolically to reach a maximum at the edges of the belt. The left hand end of each of the curves is the strain reading taken at the lower edge of the belt through the twist and the right hand end is the strain at the upper edge of the belt. It may be seen that the stress is highest at the lowermost edge of the belt, which is accounted for by the sag of the belt in this section due to the fact that it must support its own weight. This maldistribution of stress across the belt will tend to cause the belt to run toward the low tension edge as it passes over the outgoing twist pulley 30. This tendency can be counteracted by advancing the edge of the pulley toward which the belt runs by means of the adjustable pillow blocks 34.

The solid curves of Figures 7, S and 9 in each instance represent a condition of normal initial or low tension while the dotted curves in each figure represent a condition of higher tension. Thus, the pairs of curves illustrate the change in tension distribution which occurs adjacent the tail end of a conveyor when a load is applied to the upper or load carrying strand of the belt. It may be seen that the change in stress is not distributed uniformly across the belt and that in each case there is a greater variation in tension adjacent the low tension edge of the belt than there is adjacent the high tension edge, the strain on the low tension edge more nearly approximating that on the other edge when the belt is loaded. It is this unequal variation of tension and the resultant maldistribution of stress across the belt which causes the belt to fleet on the outgoing twist pulley when a load is imposed.

Correct design dictates that the minimum tension, which is imposed at the longitudinal centerline of the belt, should still be suflicient to prevent collapse of the belt or cupping through the twist section. This minimum tension is provided by weighting the vertical gravity takeup 24, and under the proper minimum tension conditions the twisted section of the belt will be straight in transverse section and free from any tendency to cup or collapse. This condition is the normal no load or initial condition of the belt and under this constant load the outgoing twist pulley 30 may be adjusted so that the belt will operate smoothly and without fleeting. v

In adjusting the guide assembly 27 the aforesaid initial conditions are first satisfied and then the vertical rolls 36 and 37 are placed in position and preferably are adjusted so as to leave a slight clearance between their peripheries and the belt surface. As the belt is loaded an increase in tension on the load carrying run results, which has been found to be transmitted around the tail pulley 31 and into the twist section adjacent the tail pulley. This variation in tension distributes itself unequally across the belt as is illustrated by the dotted curves of Figures 7, 8 and 9. Since the outgoing twist pulley 30 has already been properly adjusted for the initial or no load maldistribution of stress (the solid curves), and since the maldistribution of stress has become less severe adjacent the belt edges due to the imposition of the load (see the dotted curves), the pulley 30, is now over-adjusted and the belt will tend to run back toward the high tension or lower edge of the belt through the twist section. As the belt runs toward this high tension edge the clean side of the belt is brought into contact with the vertical roll 36 and as the fleeting continues the belt actually wraps around the roll 36 causing an increased wrapping around the outgoing twist pulley 30. The efiect of this increased wrap around the outgoing twist pulley is to tend to redistribute the stresses across the belt so that they will again return to the normal or initial stress distribution for which the belt was trained.

It may thus be seen that if the belt is normally trained with the fixed load required to insure a minimum stress greater than zero at the centerline of the belt, and'the guide assembly 27 is then adjusted with the belt in this normal condition, the imposition of a load on the carry ing strand will cause the belt to fleet at the tail end twist section so as to bring the vertical roll 36 into contact with the clean side of the belt as long as-the belt is twisted counter-clockwise when looking in the direction of belt travel. At the head end the same result is obtained by reversing the rolls, so that the rolls 36 and 37 are on the opposite belt sides from that shown in Fig.4. a

This arrangement is desirable because the major portion of the guiding of the belt may be accomplished without the use of a roller on the dirty side of the belt. The use of two rolls straddling the belt is. preferable however, since there are times, such as when the belt is started, that there will actually be less tension in the return strand than that which is imposed by the gravity takeup roll 24. Under these circumstances the fleeting action is reversed and fleet will occur in the opposite direction or in the direction which causes the roll 37 to contact the dirty side of the belt. Since the occasions when the belt will fleet toward the dirty side of the belt are generally infrequent, greater clearance may be allowed on this side of the belt between the belting surface and the roll 37 if it is desired to have the absolute minimum of rolling friction against the dirty side of the belt and if the width of the conveyor frame will permit the greater fleet without rubbing the belt edge.

The conveyor installation illustrated in Figure 1 is intended for illustrative purposes only and it should be understood that the particular arrangement of snub pulleys, takeups and feeding arrangement may be varied to suit the installation. Many changes will be apparent to those skilled in the art, and, indeed, changes will be required in different conveyor installations. This invention relates to the training and stabilization of the belt through the twist section irrespective of the path of the belt or the snub arrangement outside of the twisted sections or the number of twist sections employed. The

ingoing and outgoing twist pulleys may likewise perform other functions in the conveyor, as for example, the ingoing twist pulley may be the head pulley and the outgoing twist pulley may be the tail pulley. While counterclockwise twists have been illustrated, it should be understood that clockwise twists may be used.

To facilitate description the tail end twist section has been described in detail and it should be understood that the head end twist is similar. In Figure 1 a guide assembly is illustrated at both the head and tail end twists of the belt. Normally less stress variation due to load will be found across the belt at the head end of a conveyor than at the tail end. Further, less stress variation will be found immediately after the gravity takeup than at points spaced therefrom. Accordingly the guide assembly 27 may be omitted at the head end in some installations, particularly if the takeup is at that end; However, it will generally be found preferable to use a guide assembly in both twist sections to limit fleeting caused by transient stress variations that arise in any conveyor installation.

We claim:

1. Apparatus for training and stabilizing a twisted conveyor belt having a dirty side upon which material may be placed for conveyance and a clean side for engagement with supporting idlers, said apparatus comprising a pulley adjacent one end of a twisted portion of the belt and rotatably supported with its axis generally perpendicular to the belt centerline, means for adjusting the angular relationship between the pulley axis and the belt centerline to initially train the belt for its normal transverse stress distribution, and a guide assembly having means straddling the belt substantially centrally of its twisted portion, said means having one deflection limiting element engageable with the dirty belt side and a second deflection limiting element engageable with the clean belt side during deflection from the path for which the belt was initially trained whereby to limit the deflection of the belt from its initially trained position during changes from the aforesaid normal transverse stress distribution.

2. Apparatus for training and stabilizing a twisted conveyor belt having a dirty side upon which material may be placed for conveyance and a clean side for engagement with supporting idlers, said apparatus comprising a pulley adjacent one end of a twisted portion of the belt and rotatably supported with its axis generally perpendicular to the belt centerline, means for adjusting the angular relationship between the pulley axis and the belt centerline to initially train the belt for its normal transverse stress distribution, and a guide assembly having means straddling the belt substantially centrally of its twisted portion, said means having one deflection limiting element engageable with the dirty belt side and a second deflection limiting element engageable with the clean belt side during deflection from the path for which the belt was initially trained, the spacing between said elements being adjustable whereby to limit to a predetermined maximum the deflection of the belt from its initially trained position during changes from the aforesaid normal transverse stress distribution.

3. Apparatus for training and stabilizing a twisted conveyor belt having a dirty side upon which material may be placed for conveyance and a clean side for engagement with supporting idlers, said apparatus comprising a pulley adjacent one end of a twisted portion of the belt and rotatably supported with its axis generally perpendicular to the belt centerline, means for adjusting the angular relationship between the pulley axis and the belt centerline to initially train the belt for its normal transverse stress distribution, and a guide assembly having rolls straddling the belt substantially centrally of its twisted portion and disposed to be engageable with the dirty and clean belt sides during deflection from the path for which the belt was initially trained whereby to limit the deflection of the belt from its initially trained position during changes from the aforesaid normal transverse stress distribution, one of said rolls being removable from the guide assembly to facilitate removal of the belt.

4. Apparatus for training and stabilizing a twisted conveyor belt having a dirty side upon which material may be placed for conveyance and a clean side for engagement with supporting idlers, said apparatus comprising a pulley adjacent one end of a twisted portion of the belt and rotatably supported with its axis generally perpendicular to the belt centerline, means for adjusting the angular relationship between the pulley axis and the belt centerline to initially train the belt for its normal transverse stress distribution, and a guide assembly having a pair of rotatable rolls arranged with their axes normal to the belt centerline straddling the belt substantially centrally of its twisted portion and disposed to be engageable with the dirty and clean belt sides during deflection from the path for which the belt was initially trained, the roll adjacent the clean side of the belt having a continuous cylindrical periphery and the roll adjacent the dirty side of the belt having a discontinuous spiral shaped periphery providing a kneading action between the dirty belt side and the last mentioned roll whereby particles transferred to the spiral shaped periphery will be removed when rotated by contact with the belt.

5. Apparatus for training and stabilizing a twisted conveyor belt having a dirty side upon which material may be placed for conveyance and a clean side for engagement with supporting idlers, said apparatus comprising a pulley adjacent one end of a twisted portion of the belt and rotatably supported with its axis generally perpendicular to the belt centerline, means for adjusting the angular relationship between the pulley axis and the belt centerline to initially train the belt for its normal transverse stress distribution, a pair of rolls rotatably mounted to straddle the belt substantially centrally of its twisted portion and engageable with the dirty and clean belt sides during deflection from the path for which the belt was initially trained and a wiper arranged to contact the periphery of the roll adjacent the dirty belt side whereby to prevent an accumulation of particles picked up by said last mentioned roll during rotation in contact with the dirty side of the belt.

6. Apparatus for training and stabilizing a conveyor belt having at least two twisted portions, each in the same direction so that the dirty side of the belt does not contact the supporting idlers during the major portion of either run of the belt, said apparatus comprising a pulley rotatably supported with its axis generally perpendicular to the belt centerline, means for adjusting the angular relationship between the pulley axis and the belt centerline to initially train the belt for its normal transverse stress distribution, and guide means disposed to be engageable with the belt in one of its twisted portions and responsive to belt deflection from the path for which it was initially trained, said means being operative to limit deflection of the belt from its initially trained position during changes from the aforesaid normal transverse stress distribution.

7. A belt conveyor run comprising a first pulley having its axis substantially perpendicular to the belt centerline, said first pulley defining the transition from a non-twisted portion of the run to a first twisted section wherein the belt is inverted by means of a 180 twist, a second pulley having its axis generally perpendicular to the belt centerline and spaced longitudinally along the conveyor run from the first pulley, said second pulley defining the transition from the aforesaid twisted section to a non-twisted portion, means for adjusting the angular relationship between the second pulley axis and the belt centerline, a third pulley having its axis substantially perpendicular to the belt centerline, and spaced longitudinally along the conveyor run from the second pulley said third pulley defining the transition from the non-twisted portion of the run to a second twisted section wherein the belt is again inverted by means of a 180 twist, a fourth pulley having its axis generally perpendicular to the belt centerline and spaced longitudinally along the conveyor run from the third pulley, means for adjusting the angular relationship between the fourth pulley axis and the belt centerline and stabilizing means straddling the belt substantially medialn ly between the pulleys defining one of the twisted sections whereby to limit transverse deflection of the belt in that twisted section.

8. Apparatus according to claim 7 wherein the stabilizing means straddles the belt medially between the third and fourth pulleys whereby to limit transverse deflection of the belt in the second twist section.

9. Apparatus according to claim 8 having a takeup preceding the first pulley whereby to impose a substantially constant initial load on the conveyor run.

10. A twisted conveyor belt section comprising a first pulley defining the transition from a non-twisted section of the belt to a twisted section, the axis of said pulley being horizontal and substantially perpendicular to the belt centerline, a second pulley spaced longitudinally from the first and defining the transition from the twisted section to a non-twisted section, said second pulley having its axis horizontal and generally perpendicular to the belt centerline, means for training the belt relative to the second pulley for its normal transverse stress distribution, and deflection limiting means substantially medially between said first and second pulleys and disposed to be normally not in contact with the belt in its twisted section, but engageable with the fiat side of the belt responsive to belt deflection from its normal path, said means being operative to limit deflection of the belt from its normal path.

11. A twisted conveyor belt section comprising a first pulley defining the transition from a non-twisted section of the belt to a twisted section, the axis of said pulley being horizontal and substantially perpendicular to the belt centerline, a second pulley spaced longitudinally from the first and defining the transition from the twisted section to a non-twisted section, said second pulley having its axis horizontal and generally perpendicular to the belt centerline, means for adjusting the angular relationship between the axis of the second pulley and the belt centerline and a guide assembly having rolls straddling the belt in the twisted section substantially medially between the first and second pulleys, the axis of said rolls being substantially perpendicular to the belt centerline and the rolls being disposed to have their peripheries engageable with the belt whereby to limit belt deflection from its normally trained path.

12. Apparatus for stabilizing and limiting transverse deflection of a conveyor belt of the type having twisted sections so that the carrying side of the belt will not contact supporting idlers on the return run of the belt and located medially between twist pulleys defining the limits of said twisted belt sections, said apparatus comprising means for training the belt under conditions of normal belt stress distribution, a pair of rolls between which the medial portion of a twisted section of the belt may pass Without contacting either roll when the axis of the rolls are arranged perpendicularly to the centerline of the belt, and means mounting the rolls with their axes substantially parallel to each other and so spaced that each roll serves to limit belt deflection in the event of belt movement in a direction at right angle to its direction of travel under conditions of abnormal belt-stress distribution.

13. A stabilizing assembly for twisted conveyor belts comprising a pair of rolls having their axes substantially parallel and spaced apart a distance suflicient to pass the belt, a pair of cross members substantially perpendicular to the axes of the rolls and disposed to support the rolls in their aforesaid axial relationship, bearings rotatably supporting the rolls between said cross members, one of said rolls having a spiral shaped periphery whereby to knead the belt when contacted thereby and prevent a build-up on the spiral periphery of material picked up from the belt.

14. Apparatus according to claim 12 in which the means for mounting the rolls comprises a pair of cross members substantially perpendicular to the axes of the rolls, a pair of truss members, each arranged to support a roll in parallel axis relationship, the rolls and truss members forming a stanchion through which the belt may pass, bearings rotatably connecting the rolls to the truss members whereby the rolls may rotate when contacted by the belt, and

means for attaching said truss members to the cross memhers.

References Cited in the file of this patent UNITED STATES PATENTS 999,515 Murrock Aug. 1, 1911 2,355,448 Kratz Aug. 8, 1944 FOREIGN PATENTS 481,923 Great Britain Mar. 21, 1938 701,056 Germany Jan. 7, 1941 

